This invention relates to digitally encoding and decoding electrical signals, the background for which is fully set forth in DeFreitas U.S. Pat. No. 4,190,801 and DeFreitas et al. U.S. Pat. No. 4,254,502, both incorporated herein by reference.
In DeFreitas U.S. Pat. No. 4,190,801, an analog input signal is digitally encoded based upon the difference between that input signal and a reconstructed signal. The reconstructed signal is an analog representation of the digitally-encoded signal, and thus the reconstructed signal closely approximates the analog input signal at a slightly earlier time. Therefore, as a result of this difference comparison, changes in the analog input signal are accurately reflected in the encoded digital one.
In DeFreitas et al. U.S. Pat. No. 4,254,502, in order to enable the reconstructed signal to more accurately track a rapidly increasing or decreasing analog input signal, the reconstructed signal is generated by using a reference signal from a peak detector and an audio filter, the input to which combination is weighted by several parallel resistors. If the digital state of the encoded signal remains constant, indicating that the analog input signal is consistently either above or below the reconstructed one as it might be with a rapidly falling or rising analog input signal, more current is supplied to the audio filter through successive resistors. This increases the magnitude of the reference signal thereby increasing the absolute value magnitude of the reconstructed signal so that it closely approximates that of the actual analog signal.